Ultra-low frequency active vibration isolation system with quasi-zero stiffness characteristic using self-tuning filter-based feedforward control

Purpose of study: This study aims to resolve the compromise between low suspension stiffness and high load-bearing capability in vibration isolation and enhance the suppression performance of ultra-low frequency vibration through advanced active feedforward control methods, featuring high-performance precision isolation for large-scale ultra-precision instruments. Describe methods: An air-magnetic hybrid parallel configuration of positive and negative stiffness is employed to achieve adjustable stiffness, endowing the vibration isolation system with quasizero stiffness characteristics. A novel self-tuning feedforward control strategy is proposed through a self-tuning filter to update the controller parameters online, minimizing the loss caused by model uncertainties. Results: The vertical and horizontal natural frequencies of the system exhibit a remarkably low resonance frequency of lower than 0.5 Hz. With the self-tuning feedforward strategy, the maximum vibration attenuation reaches 78 dB in the vertical direction and 70 dB in the horizontal direction, reducing the cumulative power at 100 Hz by 61.4 % and 47.8 %, respectively. The above results showcase the proposed approach with excellent performance in isolating lowfrequency vibrations. Conclusions/Discussion: The ultra-low frequency active vibration isolation system designed in this paper achieves exceptionally low suspension stiffness. The implemented self-tuning feedforward controller isolates large precision machinery from broadband floor vibrations and significantly enhances the vibration isolation performance of the system.